Sheet supplying devices that can be incorporated in an image forming apparatus include a sheet supply tray or sheet supply cassette detachably attachable to the image forming apparatus that can accommodate an accumulated stack of recording media. The sheet supply tray is generally pulled out and inserted into a frame of the image forming apparatus through an opening formed in one side of the frame. That is, the sheet supply tray can be detachably attached in one direction only.
However, when an image forming apparatus is installed, some installation areas may have an obstacle or obstacles on the side to which the opening is provided. Therefore, in some recent approaches, a single sheet supply tray is configured to be detachably attachable to an image forming apparatus from two directions (as disclosed, for example, in Japanese Patent Application Publications Nos. 2005-255363 and 9-221236). According to this configuration, even if the sheet supply tray cannot be pulled out and inserted into the image forming apparatus from one direction, sheets or recording media accommodated in the sheet supply tray can be set from another direction.
Typically, in a configuration in which the sheet supply tray is detachably attachable to the image forming apparatus from two directions, the sheet supply tray can be slidably moved in a direction along a sheet conveyance direction and a direction perpendicular to the sheet conveyance direction. In this case, a guide mechanism is required at a position between the sheet supply tray and the frame of the image forming apparatus (containing side) to guide the sheet supply tray as it is detached from and attached to the image forming apparatus. Therefore, the frame may need to include one guide rail for guiding the sheet supply tray in the sheet conveyance direction and another guide rail for guiding the sheet supply tray in the direction perpendicular to the sheet conveyance direction.
Further, two different positioning mechanisms such as a stopper or the like for positioning the sheet supply tray when inserted in the image forming apparatus are required: One positioning mechanism for detaching and attaching the sheet supply tray in the sheet conveyance direction and another positioning mechanism for detaching and attaching the sheet supply tray in the direction perpendicular to the sheet conveyance direction.
In short, to enable detachment and attachment of the sheet supply tray with respect to the frame of the image forming apparatus in those two directions, guide rails, stoppers and other components or units for two directions may need to be provided to the frame of the image forming apparatus. This can make the configuration of the frame complicated and is not likely to make it more compact. Further, when the sheet supply tray is inserted into or removed from the image forming apparatus in one direction, the movement can be hindered by components such as a guide rail and a positioning stopper provided for movement in the other direction. Therefore, movement in both directions cannot be performed stably or reliably.